The present invention relates to a sealing device for use in contact with a reciprocating member. More particularly, the invention is concerned with a sealing device having a plurality of seal lips and suitable for use in, for example, shock absorber of an automotive suspension system. Still more particularly, the invention provides a sealing device improved to attain a higher sealing effect with reduced tightness of contact of the seal lips.
Known sealing devices of the kind described, suitable for use in automotive suspension systems, will be described with specific reference to FIGS. 8 and 9A, 9B by way of example. Referring to FIG. 8, a shock absorber 109 used in an automotive suspension system has a reciprocating piston rod 110 and a rod guide 111 which supports and guides the piston rod 110. A cap 112 is mounted so as to surround the rod guide 111. The shock absorber 109 of this type usually has a sealing device 117 which is disposed between the rod guide 111 and the cap 112. The sealing device 117 makes a sliding contact with the piston rod 110 so as to seal the internal damping fluids such as an oil OL and a gas GS which are charged inside an inner cylinder 113 and an outer cylinder 114. FIGS. 9A and 9B show Examples of the sealing device suitable for use in combination with the reciprocating member such as the piston rod 110 of the shock absorber shown in FIG. 8. The sealing device 100 shown in FIG. 9A has a seal lip 103 which makes a sliding contact with the piston rod 110 when the device is used in the shock absorber of FIG. 8 and a dust lip 104 which also makes a sliding contact with the piston rod 110. The sealing device is reinforced with an internal metal ring 106 which is embedded in the peripheral portion 105 as illustrated.
FIG. 9B shows another known sealing device 101 which is provided with a plurality of seal lips 107 which project radially inward from the main part 108 of the sealing device so as to make sliding contact with the piston rod 110 thereby attaining a sealing effect.
The sealing device 100, 101 of the kind described, particularly when used in a shock absorber of an automotive suspension system, is essentially required to develop a small friction between itself and the reciprocating member, i.e., the piston rod 110, in order to improve the comfort of the passengers on the automobile incorporating the shock absorber 109, While effectively sealing the damping fluids such as oil and compressed gas. The sealing device 101 having a plurality of seal lips 107 provides a higher sealing effect on the damping fluids such as oil and compressed gas than the sealing device 100 which has only one seal lip. The sealing device 101, however, experiences a greater friction than the sealing device 100 does. Each seal lip 107 of the sealing device 101 has two tapered surfaces 107a, 107b which converge at the apex which is resiliently collapsed when the lip 107 contacts the piston rod 110. In order to attain a higher sealing effect, these tapered surfaces 107a and 107b make different angles .alpha..sub.1 and .beta..sub.1 to the surface of the piston rod 110, the angle .alpha..sub.1 being greater than the angle .beta..sub.1. According to this arrangement, oil is almost completely prevented from entering the space 115 between adjacent seal lips 107. Although a very small amount of oil is allowed to come into the space 115, the oil is easily scraped off the space 115 during reciprocating motion of the piston rod 110, so that the oil cannot effectively serve as a lubricant.
Another problem encountered with the sealing device 101 is that the compressed gas tends to leak through a flaw in the seal lip 107 however the flaw may be slight.